In general, brackets for mounting electronic devices, such as display bracket, television bracket and projector bracket, are made to support an electronic device and adjust its height through an arm. At present, the arm-structure for height adjustment and support is achieved as follows. One end of both of the upper support and the lower support is articulated (i.e., in hinge connection) to a base, and the other end thereof is articulated to a connector. The base is provided thereon with a screw which is locked in axial direction but rotatable in a circumferential direction. A nut screw that is connected onto the screw is articulated with one end of a gas spring, and the other end of the gas spring is articulated with the upper support, so as to provide support. One end of the gas spring is made to move up and down by adjusting the screw, so that the length of one side of a triangle formed by the gas spring, the base and the upper support is varied so as to change the elastic support force of the gas spring. Since the fulcrum of the screw and the fulcrum of the gas spring are both located on the base, no matter how the arm is swinging, the fulcrum position of the gas spring remains unchanged. Additionally, there is no connection between the lower support and the gas spring as well as between the lower support and the adjusting means. The lower arm only functions to keep the swivel head horizontal when ascending or descending a device, rather than to support the device. As a result, such an arm-structure has a limited bearing capacity which is normally from 3 kg to 9 kg. When no or only a light electronic device is suspended, it is difficult to perform adjustment and the arm intends to lift up automatically. On the other hand, when a heavy electronic device is suspended, the arm intends to decline downward. Such an arm structure has a poor bearing capacity and is prone to being jammed. This in turn requires great effort to make adjustment, and the adjustment may not be smooth.